I pretty much only throw away trimmings, strips less than 1" wide, odd-shaped bits that are too wonky to be useful to me, and lousy-quality fabric that I know I'll never use. Very occasionally I'll throw away fabric that's particularly hideous-looking, but I do try to find a use for it first. (I really hate throwing anything away!)
I pass narrow strips, selvages, and crumbs on to someone else, as I usually don't have the time (or patience) to work with them.
Anything I can get a 2-1/2" square out of, I keep for my own use or save for swaps.
